1. Field of the Invention
The present invention relates to a vehicle antenna device, a vehicle including the vehicle antenna device, and a vehicle security system including the vehicle antenna device.
2. Discussion of the Background
An immobilizer system and a keyless entry system for vehicles are well known. The immobilizer system is a system in which the driver can start the engine of a vehicle with an ignition key only when the ignition key is authentic with respect to the vehicle. The keyless entry system is a system in which the driver can lock or unlock the door of the vehicle by remote control without using the ignition key.
In the immobilizer system, when the ignition key having a first transmitter built in the grip is inserted into a key cylinder of the vehicle and turned to a position, a first antenna in the vehicle receives a first signal via LF waves (e.g., from 100 kHz to 200 kHz) from the first transmitter, and the received first signal is output to the electric control unit (ECU) of the immobilizer system. The ECU starts the engine only when a first ID code in the input first signal matches a first ID code stored in advance.
In the keyless entry system, when the driver carrying a remote controller with a built-in second transmitter is within a specified range from the vehicle, a second antenna in the vehicle receives a second signal via RF radio waves (e.g., 314.9 MHz) from the second transmitter, and the received second signal is output to the ECU of a door lock device. The ECU locks or unlocks the door when a second ID code in the input second signal matches a second code stored in advance.
When the immobilizer system and the keyless entry system are applied to the same vehicle, the systems are installed separately or as one system in the vehicle, while the first and second antennas are disposed physically apart from each other.
Japanese Unexamined Patent Application Publication No. 9-275360 discloses that a ground conductor is provided on a rear of a printed circuit board and a signal processing circuit section including a transmission reception circuit is provided to a front side. A loading coil is mounted between a print pattern of the signal processing circuit section provided on the front side of the printed circuit board and a print pattern of an antenna. Furthermore, a part perpendicular to the printed circuit board of the antenna is extended from the print pattern of the antenna provided to the front side of the printed circuit board and a part of the antenna in parallel with the printed circuit board is extended from the tip of the part perpendicular to the printed circuit board of the antenna. The contents of this publication are incorporated by reference in their entirety.